1. Field of the Invention
The present invention relates to the field of gastrointestinal disorders. More specifically, the present invention discloses a method used for the treatment of acute or chronic nausea, vomiting or combination thereof in an individual by administering resiniferatoxin or derivatives.
2. Description of the Related Art
Vomiting or emesis is the expulsion of gastrointestinal contents through the mouth brought about by the descent of the diaphragm, forceful contractions of the abdominal muscles and chest wall muscles and relaxation of gastric cardia. Nausea is the behavioral and emotional state that usually leads to the unpleasant need to vomit. Nausea usually precedes and follows vomiting but it could sometimes be isolated or occur only after vomiting started. Nausea and vomiting are usually labeled acute if the symptoms were present for less than one week. Chronic symptoms usually last for more than one week.
The nausea/vomiting reflex is triggered by either peripheral or central stimuli. The peripheral stimuli activate the chemoreceptor and/or mechanoreceptors in the gastrointestinal wall. Physical damage as in inflammation and tissue injury, distension as in bowel obstruction or abnormal gastrointestinal motility as in gastroparesis activates mechanoreceptors. Toxins and culprit food contents are responsible for activating the chemoreceptor. The signal from these stimuli is carried by the afferent nerve fibers in the sensory Vagus and abdominal splanchnic nerves. These nerve fibers converge onto the vomiting center and the sensory vagus nucleus: the nucleus tractus solitaris. The vomiting center in the medulla of the brain stem is not a specific anatomical area but rather a neuronal network interconnection.
In addition to the peripheral Vagal afferents, central neuronal nerve afferent converge from the inner ear e.g. motion sickness, cranial pressure receptors e.g. meningitis, cerebral cortex e.g. psychogenic nausea and vomiting and the chemoreceptor trigger zone (CTZ). The chemoreceptor trigger zone is located in the area postrema of the fourth ventricle outside the blood brain barrier allowing it to function as a sensor for blood borne emetic stimuli including for example drugs and toxins and inflammatory mediators released during some illness. The motor Vagus nerve, other cranial nerves and the sympathetic pathway carry the efferent signal from the vomiting center. The end effect is stimulation of the salivary gland, pharyngeal, gastrointestinal and respiratory muscles to result in the coordinated event that is vomiting. Efferent nerves to the cerebral cortex and limbic system are thought to be responsible for the perception of nausea.
Chemotherapeutic and radiation induced nausea and vomiting is classically described as anticipatory, acute or delayed. Anticipatory nausea and vomiting is mediated through the central pathway as in psychogenic emesis. Acute and delayed emesis is separated by twenty-four hour cutoff. Based on the knowledge of some the neurotransmitters involved in these pathways, different pharmaceutical targets have been used to treat nausea and vomiting. This includes blocking the dopamine type-2 receptors in the chemoreceptor trigger zone and nucleus tractus solitares with agents such as prochlorperazine and metoclopramide. 5-HydroxyTryptamine subtype 3 receptors (5HT-3) are present in the chemoreceptor trigger zone and the gastrointestinal tract and it is thought that 5-HT released from the enterochromaffin cells in the gastrointestinal tract acts on 5-HT-3 receptors to initiate the vomiting reflex. Ondansetron is an example of a 5HT-3 blocker. Neurokinin-1 (NK-1) receptor blocker aprepitant inhibits the action of substance P, the ligand for NK-1 receptor. It is postulated that the nucleus tractus solitaris and the vomiting center contain NK-1 receptors and that substance P is a strong emetic. Other neurotransmitters involved in the vomiting neuro-pathway are opioids, histamine and cholinergic receptors.
Resiniferatoxin (RTX) is a naturally occurring super-analogue of capsaicin. It is found naturally in the latex of Euphorbia plants. Capsaicin (CAP) is the main pungent component in hot pepper. Resiniferatoxin and capsaicin and their analogues are exogenous ligands for the transient receptor potential cation channel subfamily V, member 1 (TRPV-1) or formerly known Vanilloid receptor 1 (VR1). The only known endogenous ligand for this receptor is the proton. TRPV-1 receptors are found on the visceral sensory nerve fibers of the unmyelinated type (C-fiber) and the thinly myelinated type (A-fiber). TRPV-1 functions as a modulator of sensory nerve responses to various noxious stimuli. Prolonged exposure to capsaicin lead to the desensitization of the TRPV1 receptors and under certain situation, complete ablation of the nerves. Resiniferatoxin induces the desensitization effect and neuronal ablation more potently than capsaicin and with minimal initial activation of the TRPV-1 neuron. Resiniferatoxin, and a number of agonists based on the structures of capsaicin and resiniferatoxin have been reported as potential analgesics through desensitization/denervation of theses neurons.
Andrew & Bhandari postulated in 1993 that resiniferatoxin had central and peripheral anti-emetic properties. Resiniferatoxin given subcutaneously had blocked the Intra-gastric copper sulphate, whole body radiation and Loperamide induced emetic response in ferrets. They proposed that resiniferatoxin acted by depletion of a neurotransmitter (Substance P) in the nucleus tractus solitarius. Andrew et al in 2000 showed that subcutaneous resiniferatoxin had initial emetic followed by anti-emetic properties in Suncus murinus, the house musk shrew. It was proposed that resiniferatoxin causes emesis by releasing Substance P at a critical site in the emetic pathway probably the nucleus tractus solitarius, and the depletion of Substance P is responsible for the subsequent anti-emetic effects. Another mechanisms that may also be involved is the desensitization of NK1-receptors by internalization of NK1-receptors Yamakuni et. al. in 2002 showed that subcutaneous resiniferatoxin in ferrets and dogs inhibited acute and delayed cisplatin and apomorphine induced emesis.
The prior art is deficient in the knowledge of the effect of local desensitization of the vagal afferents in controlling emesis as well as the anti-emetic properties for resiniferatoxin that can be achieved with local intra-gastric administration. The present invention fulfills this long standing need and desire in the art.